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# Calculator blog

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## Inverting a Matrix in HP Prime in RPN (basic!)

Three ways of inverting a matrix in RPN.

Let’s assume in M1 we have a 3x3 matrix. I took this example from Khan academy:

0 2 2

1 1 1

0 2 0

How we can invert it in RPN. I know of three different ways. Please update me if you know of any other!

• The translated from algebraic or CAS:

M1         !to the stack with Enter

inv(1)     !to express that it’ll use a single argument

• The logic from HP’s history : using the X–1 exponent key

M1         !to the stack with Enter

X–1        !much shorter than the other - but you still need to press the blue f key.

• The other possible alternative: dividing 1 by M1, with the divide “/“ key

1          !ENTER

M1       !ENTER

/

The last two imply that the functions have different operation on different days types, and implies a CAS behind,or very good programming (let’s remember that the HP15c achieved routinely several of these feats, with its excellent use of all the keyboard keys for more than one function - and in some times 3 different functions, depending on the data it was operating on (number, complex or matrix) and how the “user” flag was set)